Comparing Civics: Hybrid, Diesel, CNG, Gasoline

10 December 2004

This is a follow-on to the earlier post comparing the different powertrain versions of the Accord. Here I’m tackling four versions of the Honda Civic: Diesel (UK), Hybrid, CNG and Gasoline. The comparison isn’t quite as exact—the diesel version (from the UK) is a 5-door, the others are 4-door sedans. But close enough.

Why the focus on Honda? It’s the only carmaker with such a range of powertrains implemented in the same commercially available model.

Below we have the 2005 versions of the Civic Hybrid, the Civic 1.7 CTDi diesel, the Civic GX natural gas vehicle and the gasoline-powered Civic SE. I selected the SE to maintain the same displacement size of the engine as on the GX and diesel. There are a number of footnotes to this table, as you’ll see below. Within the “Metrics” section, I highlighted the lowest emissions and lowest fuel consumption in green.

The results? The natural gas Civic GX is by far the cleanest for regulated emissions. AT-PZEV (Advanced Technology-Partial Zero Emissions Vehicle) combines a SULEV rating for the engine with zero evaporative emissions. But the hybrid sweeps the other categories for fuel consumption, tailpipe CO2, and annual GHG emitted.

2005 Civic Hybrid

2005 Civic 1.7 CTDi

2005 Civic GX

2005 Civic SE

a. Acceleration figure is for 0-62 mph from Honda data in the UK.
b. Acceleration figure is for 0-62 mph from Honda data in the UK.
c. GX acceleration figure is for the 1998 model. Honda increased the size of the engine from 1.6 to 1.7 liters and added a CVT (Continuously Variable Transmission) in 2001. I can’t find any acceleration data for this model, and Honda doesn’t provide such.
d. Fuel consumption for CNG is converted to gallons gasoline equivalent (GGE).
e. CO2 data from Honda UK.
f. CO2 data from Honda UK.
g. Calculated using 1.74 kg CO2/liter gasoline equivalent.
h. Calculated using 2.32 g CO2/liter.
i. EPA GHG annual emissions presented are full fuel-cycle estimates including carbon dioxide, nitrous oxide, and methane. Full fuel-cycle estimates consider all steps in the use of a fuel, from production and refining to distribution and final use.

Engine

Fuel

Gasoline

Diesel

CNG

Gasoline

Type

I-4

I-4

I-4

I-4

Displacement (liters)

1.3

1.7

1.7

1.7

Power: kW
(hp)

63(85)

74(99)

75(100)

95(127)

Torque: Nm(lb-ft)

118(87)

219(162)

133(98)

154(114)

BMEP: psi

160.4

240

145.2

145.2

Electric Motor

Power Output: kW(hp)

10(13.4)

NA

NA

NA

Torque: Nm
(lb-ft)

49(36)

NA

NA

NA

Metrics

Acceleration 0-60 (seconds)

12.8 a

11.5 b

11.9c

9.4

Combined mpg (US)
(liters/100km)

47(5)

37(6.3)

32 d(7.4)

34(6.9)

Emissions rating

SULEV

EURO III

AT-PZEV

ULEV

Tailpipe CO2 g/km

116 e

134 f

129 g

160 h

EPA Annual GHG Emissions: i tons

4.0

–

5.1

5.7

Unlike the Accord hybrid, which is weighted more toward performance, the Civic hybrid sacrifices quickness (it has the slowest acceleration of the four) for fuel efficiency. The downsized 1.3-liter gasoline engine in the Civic hybrid allows it to deliver the lowest fuel consumption of the four, and hence the lowest amount of CO2 and greenhouse gases.

The diesel in the CDTi is from Isuzu, and isn’t at the head of the competitive pack in terms of performance or emissions. Honda’s in-house i-CDTi for the Accord delivers much better. Nevertheless, as expected in a diesel, the Civic CDTi consumes less fuel and produces fewer CO2 emissions than its gasoline counterpart. The story is not at all as good on the criteria emissions side, though, with the CDTi ranked only at Euro III levels. Euro III allows twice the level of NOx (0.50 g/km vs. 0.25 g/km) and PM (0.05 g/km vs. 0.025 g/km) as Euro IV.

The Civic GX is the cleanest of the four in terms of criteria pollutants. Emissions created during combustion are dependent partly upon the chemical compositon of the fuel, and natural gas has a much simpler, and lower-carbon, chemical structure than gasoline or diesel. It also has a lower energy content and so requires additional fuel consumption for equivalent performance, as you can see in the chart above. While the baseline gasoline SE consumes 6.9 liters of gasoline for every 100 kilometers driven, the GX requires 7.4 liters gasoline equivalent.

Despite this higher fuel consumption, however, the GX emits less tailpipe CO2 than its gasoline counterpart—again, because of the difference in composition of natural gas vs. gasoline. Note the EPA calculation of annual greenhouse gas emissions. This represents the full fuel lifecycle—production through consumption—and so factors in processing, transportation and the like. On a full fuel lifecycle basis, the emissions overhead associated with natural gas production and transportation reduces the advantage at the tailpipe the natural gas car has over the gasoline. All are easily bested by the Civic Hybrid, which, although it has a gasoline engine, just burns much less fuel.

The transmission type makes a huge difference in real world mpg. The manual clutch is the best, because it is direct drive. The CVT has slippage at highway speeds, but is more efficient than an automatic torque converter.

I'm amazing how little attention is paid to the gearbox and driving dynamics. throwing away 5-8% with the automatic before any hybrid or engine benefits and the CVT loses on the top end.

The key factor in driving dynamics is the 40-60 mph acceleration, which if the gearbox is slipping, as opposed to being in the right gear, loses momentum - requiring lots of power to get going again - more gas.

Seems like a trade-off between hydrocarbons & particulates released from longer chain fuel molecules, verses lower energy content and increased GHG emissions from CNG. Why not plug-in hybrid diesel? The VW Wundercar II (scirocco-style hybrid) is slated to get 120mpg - with plug-in capacity and running on biodiesel, CO2 would be down about 80% and urban emissions would be minimized (along with increased efficiency).

Can anybody please tell me what is going on with the Wundercar II? It was supposed to come out by this year, but hasn't. And VW isn't saying anything!!!! Anyone with any info on this vehicles release date or any other info?

In all the "hybrid v diesel v conventional" discussions, I haven't seen any mention of the Miller Cycle engine: up to 25% decrease in fuel consumption without sacrificing performance (or, 25% increase in performance with no increase in fuel consumption). The only production Miller Cycle vehicle I know of was a Mazda Millenia, back around 1999-2000. Simpler, less complicated than a hybrid, with equivalent efficiency gains.
I still favor diesels. Biodiesel is almost greenhouse-neutral, vegoil and WVO are greenhouse-neutral.

Seems to me your analysis is flawed. Rather than selecting the SE to maintain the same displacement you should pick a smaller motor to maintain the same performance rating. Gas engines are more efficient in terms of power delivery than their diesel cousins.